为发出的 HTTP 请求在不同阶段添加事件监听器。事件监听器可以接收到请求的详细信息,也可以修改或取消请求。



在请求过程中的任意时间,onErrorOccurred (en-US) 可以被触发。虽然有时候触发的事件顺序不同,举个例子,在火狐浏览器中的 HSTS 过程,在 onBeforeRequest 事件执行后,onBeforeRedirect 事件会被立即触发。

所有的事件,接受onErrorOccurred事件, addListener()有三个参数 :

  • 监听本身
  • 一个filter 对象,所以你仅可以被特定请求或特定的资源类型提醒
  • 一个可选的extraInfoSpec对象。你可以使用这个对象添加特定的事件命令

这个监听函数接收一个details对象,这个对象包含这个请求的信息。他包含一个请求 ID, 在插件中这个 ID 可以关联唯一个请求事件。这个 ID 是浏览器会话和插件上下文中唯一的。他始终在同一个请求中,贯穿着转发和授权等事件中。

在一个给定的主机上使用 webRequest API, 你必须有这个主机的相关权限,包括"webRequest" API permission 和 host permission. 为了使用 "blocking" 特性,你必须有 "webRequestBlocking" API 权限。

这个 webRequest API 不能让你进入一些安全敏感的请求,比如update checks and OCSP checks.

Modifying requests


为了完成这些操作,你需要在extraInfoSpec参数中添加"blocking"的值到事件的addListener()。这将使得监听器变成同步执行。在监听器中,你可以返回一个表明需要作修改的BlockingResponse (en-US)对象:比如说,你想要发送的修改后的请求头。

从 Firefox 52 开始,监听器会返回一个resolve(BlockingResponse) 的 Promise,而不是直接返回一个BlockingResponse。这使得监听器可以异步地处理请求。


webRequest.ResourceType (en-US)
Represents a particular kind of resource fetched in a web request.
An object describing filters to apply to webRequest events.
webRequest.HttpHeaders (en-US)
An array of HTTP headers. Each header is represented as an object with two properties: name and either value or binaryValue.
webRequest.BlockingResponse (en-US)

An object of this type is returned by event listeners that have set "blocking" in their extraInfoSpec argument. By setting particular properties in BlockingResponse, the listener can modify network requests.

webRequest.UploadData (en-US)
Contains data uploaded in a URL request.


The maximum number of times that handlerBehaviorChanged() can be called in a 10 minute period.


webRequest.handlerBehaviorChanged() (en-US)
This function can be used to ensure that event listeners are applied correctly when pages are in the browser's in-memory cache.


webRequest.onBeforeRequest (en-US)
Fired when a request is about to be made, and before headers are available. This is a good place to listen if you want to cancel or redirect the request.
webRequest.onBeforeSendHeaders (en-US)
Fired before sending any HTTP data, but after HTTP headers are available. This is a good place to listen if you want to modify HTTP request headers.
webRequest.onSendHeaders (en-US)
Fired just before sending headers. If your add-on or some other add-on modified headers in onBeforeSendHeaders (en-US), you'll see the modified version here.
webRequest.onHeadersReceived (en-US)
Fired when the HTTP response headers associated with a request have been received. You can use this event to modify HTTP response headers.
webRequest.onAuthRequired (en-US)
Fired when the server asks the client to provide authentication credentials. The listener can do nothing, cancel the request, or supply authentication credentials.
webRequest.onResponseStarted (en-US)
Fired when the first byte of the response body is received. For HTTP requests, this means that the status line and response headers are available.
webRequest.onBeforeRedirect (en-US)
Fired when a server-initiated redirect is about to occur.
webRequest.onCompleted (en-US)
Fired when a request is completed.
webRequest.onErrorOccurred (en-US)
Fired when an error occurs.

Browser compatibility

BCD tables only load in the browser

Edge incompatibilities

BCD tables only load in the browser

Promises are not supported in Edge. Use callbacks instead.

Example extensions


This API is based on Chromium's chrome.webRequest API. This documentation is derived from web_request.json in the Chromium code.

Microsoft Edge compatibility data is supplied by Microsoft Corporation and is included here under the Creative Commons Attribution 3.0 United States License.